For brake cylinders for vehicles, which comprise not only a service brake but also a parking brake, it is known to constitute the parking brake as a spring-loaded brake. Such spring-loaded brakes apply as soon as the releasing pressure loses pressure, i.e., they are held in release position by the release pressure of a pneumatic or hydraulic pressure medium and are moved into the braking position when the pressure drops due to spring tension. The result of this drop in pressure is that, in the case of rail vehicles, automatic braking is necessary if the pressure of the pressure medium system should fail.
In addition, brake cylinder constructions with a spring-loaded member are known in which said spring-loaded member can be locked with a pawl mechanism, and thus cannot be released automatically. The pawl mechanism is disengaged through a special pressure circuit when the parking or spring-loaded brake is to be applied. The drawback of such designs is that, to clamp the spring-loaded member, a minimum pressure must be attained in order to release the brake. Even disengaging the spring-loaded member under load is problematic.
Finally, in the case of caliper designs, directly acting cylinders are known, i.e., service brake cylinders with parallel operating parking brake cylinders, wherein two pressure circuits are used independently of one another. However, such a combination of a service brake or active cylinder with a parking brake cylinder arranged parallel thereto is possible only with the advantageous design features of caliper constructions. In the case of caliper designs, such combinations are problematic with respect to construction space and synchronizing the function.